The bioavailability of carotenoids from diets can be affected by a complex number of factors such as physicochemical properties of the various carotenoids (free vs. esterified; hydrocarbon vs. oxygenated); their physical state (crystals vs. protein bound vs. solubilized in oil); dietary factors, e.g. amounts and types of fat and fiber; nutritional and physiologic status of the subject, and genotype. Additionally, carotenoid interactions at the intestinal level may reduce absorption of either of the carotenoids. Competition for absorption may occur at the level of micellar incorporation, intestinal uptake, lymphatic transport, or at more than one level. For example, beta-carotene was reported to decrease lutein absorption, whereas lutein decreased beta-carotene absorption in some human subjects but increased it in others (See Kostic D, White W S, Olson J A. Intestinal absorption, serum clearance, and interactions between lutein and β-carotene when administered to human adults in separated or combined oral doses. Am J Clin Nutr. 1995; 62:604-610). In another study, lutein impaired beta-carotene absorption by human subjects but did not affect the secretion of retinyl esters in chylomicrons (See van den Berg H, van Vliet T. Effect of simultaneous, single oral doses of 13-carotene with lutein or lycopene on the β-carotene and retinyl ester responses in the triglyceride-rich fraction of men. Am J Clin Nutr 1998; 68:82-89). In contrast, beta-carotene absorption was not affected by lycopene in these subjects. Additional reports of interactions between pure carotenoids that affect their postprandial appearance in plasma of humans and animals have been reviewed by van den Berg (See van den Berg H. Carotenoid interactions. Nutr Rev. 1999; 57:1-10.). Tyssandier et al. reported that the absorption of beta-carotene, lutein, and lycopene from a single vegetable was greater when the food was administered alone than when it was co-administered with either a second carotenoid-rich vegetable or the purified carotenoid that was enriched in the second vegetable (See Tyssandier V, Reboul E, Dumas J, Bouteloup-Demange C, Armand M, Marcand J, Sallas M, Borel P. Processing of vegetable-borne carotenoids in human stomach and duodenum. Am J Physiol (Gastrointest Liver Physiol). 2003; 284:G913-G922).
Early studies have reported that both the canine and domestic feline are unable to absorb beta-carotene from the diet (Goodwin T. Mammalian carotenoids. In: Goodwin T W, ed. The comparative biochemistry of the carotenoids. London: Chapman and Hall Ltd., 1952; 229-269). Recently, several systematic studies indicated that dogs and cats can absorb beta-carotene and lutein (Weng B C, Chew B P, Park J S, Wong T S, Combs R L, Hayek M G, Reinhart G A. β-Carotene uptake by blood plasma and leukocytes in dogs. FASEB J 1997; 11:A180 Kim H W, Chew B P, Wong T S, Park J S, Weng B B, Byrne K M, Hayek M G, Reinhart G A. Dietary lutein stimulates immune response in the canine. Vet Immunol Immunopathol. 2000 May 23; 74(3-4):315-27. Chew B P, Weng B C, Park J S, Wong T S, Combs R L, Hayek M G, Reinhart G A. Uptake of β-carotene by blood plasma and lymphocytes in cats. FASEB J 1997; 11:A447. Kim, H. W., Chew, B. P., Wong, T. S., Park, J. S., Weng, B. C., Byrne, K. M., Hayek, M. G. & Reinhart, G. A. Modulation of humoral and cell-mediated immune responses by dietary lutein in cats. Vet. Immunol. Immunopath. 2000, 73:331-341). However, it is unknown how carotenoids interact with each other in dogs and cats. A beneficial effect between the carotenoids is desired if used in companion animals because it is believed that each individual carotenoid has a potential role in contributing to the health of dogs and cats. Thus, a product is desired that would combine carotenoids in a way to positively affect the absorption of those carotenoids. Such a product could then exhibit more beneficial effects on the animal.